1) Field of the Invention
The present invention relates to anchors intended to be incorporated into a concrete component prior to casting, for example lifting anchors to provide a lifting point by which the component can be lifted during subsequent erection, and anchors for providing a fixing point for other components post-erection.
2) Description of the Prior Art
Concrete lifting systems for lifting of concrete panels, beams and other components typically involve the use of lifting anchors incorporated into the component during casting, with the head of the anchor being encased within a removable or disposable hollow void former to form within the surface of the component a recess within which the head of the anchor lies for releasable coupling to lifting equipment.
Different types of lifting anchor are required for different components, loads, and type of lift. FIG. 1 shows an anchor which has been widely used for edge lifting of concrete panels although it can also be used for edge lifting of other components. As shown in FIG. 1 the anchor comprises opposed parallel legs 2 of wave like or meandering form extending from a head 4. The particular head shown is designed for use with a releasable lifting clutch in the form of a ring clutch having an arcuate locking bolt received within an eye 6 in the head and which remains exposed within the recess after casting. Typically, this type of anchor is formed from a thick metal plate using non-contact high energy cutting means such as a laser beam or plasma arc.
As mentioned, anchors of the type shown in FIG. 1 have a principal utility in the edge lifting of concrete panels and in that usage the anchor is installed within the panel such that it traverses the thickness dimension of the panel with each of the two legs 2 lying adjacent to the respective faces of the panel. The two legs 2 lie either side of reinforcing mesh in the central median plane of the panel and one or more shear bars or tension bars are incorporated into the apertures 8 shown in the head in order to tie the anchor into the reinforcing structure of the panel; the details of the actual tie-in will depend on the actual loading to which the anchor is to be subjected and also to the type of lift which can be either straight edge lift or edge lift with tilt-up.
When installed, there is a relatively small thickness of concrete between each leg 2 and the adjacent face of the panel. During lifting, the meandering profile of the leg interacting with the concrete to the inside and outside of the leg provides on the leg opposing lateral forces which are normally in equilibrium in order to prevent lateral deflection of the leg. However a potential failure mode with this type of anchor arises if the strength of the concrete to the outside of the leg is insufficient to withstand the forces acting on the leg from its inner face and acting in a sense to force the leg outwardly. If such failure were to arise, the leg would be deflected outwardly and would “burst through” the adjacent face of the panel. In order to avoid this type of failure, existing anchors of this type are designed with legs which are sufficiently long to provide load distribution over a long leg length such that “burst through” in the circumstances just described, should not arise.
With existing anchors of this type, the need to produce the anchor with relatively long legs increases the material costs and also can sometimes complicate the installation of the anchor prior to casting.